1. Field of the Invention
The invention concerns a device for transferring or transmitting ultrasonic energy into a fluid or pasty medium, and with the further, characteristics particular to this species of invention. A device of this type is known from U.S. Pat. No. 4,016,436.
2. Description of the Related Art
In this known device a wave guide is provided on one side of a tubular shaped cavity resonator which, by means of a piezo-electric transducer, which for its part converts electrical alternating current output signals of an alternating current generator into longitudinal mechanical oscillations, is capable of being brought or excited to resonant longitudinal oscillations. On a flange shaped area on this transducer the cavity resonator is mechanically rigidly connected and acoustically coupled.
In a further device of the above described type (U.S. Pat. No. 5,200,666), which is substantially a functional analog of the first described, respective transducers transmit ultrasound energy at both ends of a tubular resonator, which is designed for conversion of longitudinal oscillations into transverse oscillations.
It is also known (U.S. Pat. No. 4,537,511), to use a tubular cavity resonator, which is closed on both ends and from one side is impinged by ultrasound from a coupled transducer.
In all these devices the length of the tubular cavity resonator is almost always selected to be in a first approximation described according to the equation, EQU L=nc.sub.0 /2f.sub.r (1)
in which n represents a whole number, with c.sub.0 being the oscillation frequency in a steel type resonator and with f.sub.r being the mechanical resonance frequency of the wave guide utilized for introduction of ultrasound in the resonator and which is acoustically coupled with the transducer. The oscillation frequency c.sub.0, is here described by the relationship, ##EQU1## in with E being the modulus of elasticity (Youngs modulus) and with .rho. being the specific weight of the resonator material.
In order, in such ultrasound devices, to convert the greatest possible proportion of electrical energy into utilizatable sound energy, it is also known (FR-A-2 354 827 and EP-A-0 044 800), to so attempt to arrange or design the cavity resonator, so that the longitudinal as well also the transverse natural oscillating frequency of its jacket satisfies the resonance conditions.
In such devices the oscillating effective element is constructed as a three dimensional tubular cavity resonator, in which the propagation velocity V.sub.x and v.sub.r, and therewith also the wave lengths .lambda..sub.x and .lambda..sub.r of the oscillations, which are associated with deflection in the direction of the longitudinal axis (x-direction) and radial thereto, are necessarily different. Those respective ultrasound waves, of which the deflection is in the direction of the longitudinal axis (x-direction) of a resonator, of which the axial length is selected to correspond to a whole number multiple of the half wave length (.lambda..sub.x /2), do not contribute to the outward radiation of ultrasound energy, however prevent a buildup of ultrasound energy and facilitate a good even form or shape of the distribution of the ultrasound energy over the total-axial-resonator length, while those ultrasound waves, of which the oscillation form of the resonator corresponds with deflection radial to the resonator-length axis and to its outer surface, mediate an effective radiating out of ultrasound energy in the environment.
Such an arrangement or design, given that the characteristics of the resonator wall material are pre-determined, requires a very precise coordination of the geometric dimensions of the resonator, namely its length L, its outer diameter D.sub.0 and its wall thickness .delta.. This relationship can in the case of pre-determined values of the outer diameter D.sub.0 and the wall thickness .delta. of course be achieved by adaptation or adjustment of the resonator length L, which however as a rule requires time consuming experiments or testing and only then is justifiable, when a subsequently larger number of such devices can be built following this experimentation to determine optimal length. Special devices which are only constructed in small quantities are thus very expensive.
From DE-33 16 353 A1 it is known, in connection with a cleaning device, in which the material to be cleaned, for example a length of textile material, is exposed to an ultrasound field, to use a so-called broad horn for transmission our application of ultrasound into a fluid bath through which the length of textile material is transported, which by means of an ultrasound transmitter corresponds is excited to resonate both in the longitudinal direction--the excitation direction--as well also in the thereto right angled transverse direction, in which the expansion or spreading of the broad horn corresponds at least approximately to the breadth of the textile material to be cleaned corresponds. This broad horn is designed as a flat rod-shaped, massive transmission body ("Sonotrode"), which corresponds in the excitation direction measured length to the half ultrasound-wave shape (.lambda./2) and in transverse direction measured breadth corresponds to a whole number multiple of this value; the thickness of the plate shaped broad horn measured between the broad longitudinal surface is significantly smaller than the half ultrasound wave length, which in longitudinal-and transverse direction has the same value. Through this dimensioning of the broad horn there should, which in principle is also possible, over the total breadth (n.multidot..lambda./2) an even shaped broadcasting characteristic of the broad horn and therewith also be achieved the even good cleaning of the length of material; however, the Q-factor (usable ultrasound-energy/electrical excitation energy), in comparison with ultrasound devices, which work with hollow space resonator-excitation, is comparatively small, so that very high output and correspondingly expensive ultrasound transmitters must be utilized, which makes the operation of this known type of cleaning device, which works with block-shaped massive broadcast elements, significantly more expensive.
It is the object of the invention, beginning with a device of the type known in the art, to provide a design of a device which produces a desirable high transmission operating effectiveness, and, after it has once been designed, does not, or at least not to any significant degree, have a post-working or reworking requirement, in order to be configured for a operation with optimal working effectiveness, and in particular to provide a device, which with a predetermined construction and type of coupling or transmission provided for excitation to oscillation, for its part by a transducer driven wave guide on a hollow tubular cavity resonator functions with a operating effectiveness which is a close to the optimal operating effectiveness.
This task is solved for devices in which the tubular cavity resonator is "strongly", that is mechanically substantially rigidly, coupled with the wave guide, according to the characterizing portion of Patent claim 1, thereby that the resonator length L is selected according to the relationship the formula ##EQU2## wherein with v the Poisson transverse contraction co-efficient of the tubular cavity resonator-material, with .delta. the wall thickness of the tubular cavity resonator and with D.sub.0 the outer diameter of the tubular cavity resonator are indicated.
The hereafter provided deviations from the relationship or equation (1) can be very small, so that the equation or relationship (2) with respect to the relationship for equation (1) produces only a minimal improvement, but can however in practical cases also deviate by about approximately 40% from the result obtainable through the relationship (1), so that, in comparison with such a case, the construction according to the relationship (2) produces a substantially better result.
In a preferred embodiment of a device according to the invention there is a "weak" coupling of the tubular shaped cavity resonator and the wave guide provided, wherein weak coupling means that between the resonant oscillations of the cavity resonator, on the one hand, and the resonating-longitudinal-oscillations of the wave guide, on the other hand, a significant phase difference exists. Such a weak coupling can for example be realized thereby, that the wave guide is swingingly or flexible coupled with the cavity resonator via a yieldable spring element, which may have the form of a disc spring, is pivotably coupled with the cavity resonator. For this case, in which the wave guide must have in advance carried out a multiplicity of longitudinal oscillations, before the hollow cavity resonator is brought into resonance, that is, oscillates with maximal amplitude, the length L.sub.w thereof is provided according to the relationship ##EQU3## when at the same time or simultaneously the ultrasound is coupled into the resonator only from one side.
For a likewise given case of weak acoustic coupling between the cavity resonator and the wave guide, wherein the cavity resonator is acted upon from both its ends equiphasally with oscillation energies produced by two transducers, its length L.sub.w is determined by the relationship ##EQU4##
By the characteristics of claims 4 through 6 conditions are given, in which satisfaction of the oscillation form of the cavity resonator is completely radially symmetrical (symmetry group C.sub..sub..infin.), that is, the radial deflections in the plane extending at right angle to the central longitudinal is always equiphasic, or as the case may be the resonator in each transverse section plane is circular shaped, the cross-section of this circle however along the length of the resonator is spatially periodically varied, and in each cross-sectional plane of the resonator diameter time-wise varies periodically.